Drug delivery devices have application where regular injection by persons without formal medical training occurs. This may be increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. In practice, such a drug delivery device allows a user to individually select and dispense a number of user variable doses of a medicament.
There are basically two types of drug delivery devices: resettable devices (i.e., reusable) and non-resettable (i.e., disposable). For example, disposable drug delivery devices are supplied as self-contained devices. Such self-contained devices do not have removable pre-filled cartridges.
Rather, the pre-filled cartridges may not be removed and replaced from these devices without destroying the device itself. Consequently, such disposable devices need not have a resettable dose setting mechanism.
A further differentiation of drug delivery device types refers to the drive mechanism: There are devices which are manually driven, e.g. by a user applying a force to an injection button, devices which are driven by a spring or the like and devices which combine these two concepts, i.e. spring assisted devices which still require a user to exert an injection force. The spring-type devices involve springs which are preloaded and springs which are loaded by the user during dose selecting. Some stored-energy devices use a combination of spring preload and additional energy provided by the user, for example during dose setting. Further types of energy storage may comprise compressed fluids or electrically driven devices with a battery or the like.
These types of delivery devices generally comprise of three primary elements: a cartridge section that includes a cartridge often contained within a housing or holder; a needle assembly connected to one end of the cartridge section; and a dosing section connected to the other end of the cartridge section. A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication (e.g., insulin), a movable rubber type bung or stopper located at one end of the cartridge reservoir, and a top having a pierceable rubber seal located at the other, often necked-down, end. A crimped annular metal band is typically used to hold the rubber seal in place. While the cartridge housing may be typically made of plastic, cartridge reservoirs have historically been made of glass.
The needle assembly is typically a replaceable double-ended needle assembly. Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge assembly, a dose is set, and then the set dose is administered. Such removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly.
The dosing section or dose setting mechanism is typically the portion of the device that is used to set (select) a dose. During an injection, a plunger or piston rod contained within the dose setting mechanism presses against the bung or stopper of the cartridge. This force causes the medication contained within the cartridge to be injected through an attached needle assembly. After an injection, as generally recommended by most drug delivery device and/or needle assembly manufacturers and suppliers, the needle assembly is removed and discarded.
The dosing section of drug delivery devices for selecting and dispensing a number of user variable doses of a medicament often comprises a display for indicating the selected dose to a user. This is especially important where a user may select a different dose each time depending on the state of health. There are mechanical displays, e.g. a drum with printed numbers on its outer surface, wherein the number corresponding to the actually selected dose is visible through a window or opening in the device. Although such mechanical displays are simple and reliable, they usually require a relatively large construction space which makes the devices bulky. In addition, the size of the numbers is in some cases too small for visually impaired users. Further, electronic displays are known, e.g. LCD displays, which have the benefit of a relatively large number size without requiring too much construction space. However, a downside of electronic displays is that they require an energy source and that such electronic components may be too expensive, especially in a disposable drug delivery device.
A disposable drug delivery device is known from WO 2004/078241 A1, wherein the display comprises a number sleeve with numbers printed on its outer surface. The device further comprises a housing, a cartridge holder for retaining a cartridge containing a medicament, a piston rod displaceable relative to the cartridge holder, a driver coupled to the piston rod, a dose setting knob coupled to the driver and fixed to the number sleeve, and an injection button. The number sleeve is in threaded engagement with the housing, such that the number sleeve rotates along a helical path in a first direction during dose selecting and rotates back into the housing in a second, opposite direction during dose dispensing.
Further, WO 2010/046394 A1 discloses a dial mechanism for an injection device comprising a ring with a plurality of teeth having a steep edge in one direction and a sloped edge in the opposite direction. Due to this design of the teeth, a ratchet arm of a ratchet tube is prevented from rotating in one direction and allowed to rotate in the opposite direction. For dose correction the ratchet arm may be pulled out of engagement with the teeth by rotation of a reset tube. This results in rotation of the ratchet tube relative to the ring driven by a torsion spring. Due to the size of torque of the spring, the ratchet tube will move faster than the reset tube, such that the ratchet arm will flex to its initial position resulting in re-engagement of the arm with the next steep tooth edge. Repeatedly urging a ratchet arm in and out of engagement with ratchet teeth by a reset tube may result in failure of the ratchet arm and/or the reset tube, especially if relatively cheap plastic components are used as may be the case in disposable devices. In addition, a ratchet tube and a reset tube require a relatively long device which may have ergonomic drawbacks.
WO 2006/045526 A1 discloses a pen-type drug delivery device having a dose setting member with an opening defining a cam surface an a cam follower which is an integral part of a ratchet. Rotation of the dose setting member in a first direction entrains the cam follower, whereas rotation of the dose setting member in the opposite direction lifts the cam follower thereby decoupling the ratchet.
WO 2014/052676 A1 and WO 2012/089445 A1 disclose devices with a flexible piston rod comprising several toothed elements.